1. Field of the Invention
The present invention relates generally to apparatus and methods for forming fibers and capillary tubing which have a protective coating. More particularly, the present invention relates to apparatus and methods for continuously forming glass fibers or capillary tubing and immediately protecting the glass surface with a sputter deposited coating of metal, metal alloy or other protective material. The present invention also relates to an improved sputter coating apparatus.
2. Description of Related Art
Glass fibers and capillary tubings are widely used in applications ranging from optical communication systems to analytical equipment such as gas chromatographs. Glass fibers are widely used as optical waveguides because they can be formed with specific optical qualities and physical characteristics. Due to the wide variety of environments to which fiber optical waveguides are exposed, it is important in many instances that the fiber surface be coated with a protective material. In particular, the fiber surface must be protected from moisture which would degrade the strength of the fiber. The protective coatings range from metals and metal alloys to various oxides and polymers.
Glass capillary tubing is also widely used in a number of applications. One common use for glass capillary tubing is for gas chromatograph columns. Protective coatings applied to the glass capillaries provide increased strength. This feature is particularly important with respect to gas chromatography columns which are typically over 100 meters long and require frequent handling during installation and removal from chromatography units.
The molten dip method is a common procedure used to coat glass fibers or capillary tubings with a protective metal layer. The molten dip method involves continuously pulling the fiber through a molten pool of metal immediately after it emerges from the drawing furnace. The molten pool of metal is located sufficiently close to the emerging fiber so that the pristine glass fiber surface does not become contaminated prior to coating with metal. This is important since it is undesirable to allow contaminants to form on the glass surface prior to application of the protective coating.
The molten dip method is well suited for its intended purpose; however, the method is limited in utility because only materials having a melting temperature below the melting point of the glass can be utilized. Additionally, the molten form of the metal or other coating material must possess the appropriate surface tension and adhesion properties to achieve a uniform hermetic seal. Another problem with the application of a molten layer to the glass fiber or capillary tubing is the high microbend induced optical attenuation which results from the large thermomechanical stresses created during the coating process.
In view of the above considerations, it would be desirable to provide an alternative process for applying protective coatings to glass fibers or capillaries wherein the limitations of the molten dip method are eliminated while still providing immediate and continuous coating of the glass fiber as it is formed.